Lighting device and projector

ABSTRACT

The present invention provides a lighting device that has two lamp units and is suitable for a light source of a projector-type display apparatus to realize bright illumination, and also a projector-type display apparatus with such a lighting device incorporated therein. The lighting device includes a light source unit and an integrator optical system and enables an illumination area to be illuminated uniformly and evenly with the light emitted from the light source unit and transmitted via the integrator optical system. The light source unit includes a pair of lamp units arranged in parallel, and a reflector of each lamp unit has a contour with both sides cut off. The pair of lamp units are preferably arrayed in a direction perpendicular to a longitudinal direction of the illumination area. This structure realizes a small-sized, compact lighting device with a high quantity of output light. Application of such a lighting device to the projector-type display apparatus enables uniform and bright projection images to be produced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compact, small-sized lighting deviceincluding at least two lamp units and having a high utilizationefficiency of light. The present invention also pertains to aprojector-type display apparatus with such a lighting device forproducing bright projected images which are uniform in brightness.

2. Discussion of the Background

A lighting device incorporated in projector-type display apparatusgenerally has a lamp unit, which includes a light source lamp, such as ahalogen lamp or a metal halide lamp, and a reflector for reflecting anincident ray emitted from the light source lamp and outputting thereflected ray as a parallel beam or a converging beam in a predetermineddirection. Available reflectors have the reflecting surfaces in theshape of paraboloid or ellipsoid.

It is preferable that the lighting device used in the projector-typedisplay apparatus has a large output quantity of light, in order toproduce uniform and bright projected images. Further a compact,small-sized lighting device is desirable when being incorporated inportable projector-type display apparatus.

The lighting device may include a plurality of lamp units, for example,two lamp units, in order to increase the output quantity of light. Asimple array of the two lamp units in parallel, however, doubles thewidth of the lighting device and makes the lighting device undesirablybulky. This arrangement also doubles the width of the flux of outputlight and requires an extended width of the optical path in the lightingdevice. This further doubles the required width of the optical pathformed in the projector-type display apparatus with such a lightingdevice incorporated therein. This arrangement is thus not suitable forthe requirement of the compact, small-sized structure.

A typical example of the lighting device incorporated in theprojector-type display apparatus is a lamp unit including a light sourcelamp having a short arc length and a reflector of a paraboloidal shapehaving a short focal distance. The distribution of the quantity of lightemitted from the lamp unit of this structure is shown as acharacteristic curve that has a sharp peak on and in the vicinity of alamp optical axis and abruptly decreases with a distance from the lampoptical axis. The use of only the light fluxes in a central portionincluding the lamp optical axis for illumination does not significantlylower the quantity of light.

SUMMARY OF THE INVENTION

The object of the present invention is thus to provide a technique forproviding a lighting device with a plurality of lamp units and aprojector-type display apparatus with such a lighting deviceincorporated therein, which can produce projection images that arebright, uniform in brightness, and even in color.

(First Lighting Device and Projector-type Display Apparatus therewith)

At least part of the above and the other related objects is attained bya first lighting device of the present invention, which includes a lampunit having a light source lamp and a reflector for reflecting lightemitted from the light source lamp, the lighting device furtherincluding a plurality of the lamp units arrayed in a directionperpendicular to an optical axis of the light source lamp, wherein thereflector of each the lamp unit has a shape obtained through cutting aconcave surface of reflection on at least one end adjoining to anotherlamp unit by a plane substantially perpendicular to a direction of thearray of the lamp units.

The plurality of lamp units may be arrayed in one directionsubstantially perpendicular to the optical axis of the light sourcelamp, or in two directions each substantially perpendicular to theoptical axis of the light source lamp.

In a lamp unit with a reflector, the quantity of output light isextremely large in a central portion including an optical axis of alight source lamp and decreases with a distance from the optical axis ofthe light source lamp.In the first lighting device of the presentinvention, the reflector of each lamp unit is cut to have a narrowwidth. This reduces the total width of the lighting device. Thisstructure with narrow reflectors effectively utilizes the output lightin the central portion including the lamp optical axis and therebyensures a sufficient amount of output light. The lighting device of thepresent invention ensures a greater quantity of output light, whilehaving substantially the same size as that of the conventional lightingdevice with only one lamp unit. The lighting device of the presentinvention is preferably used as a light source of a projector-typedisplay apparatus that displays bright projection images.

In accordance with one preferable application, the reflector has a shapeobtained through both ends of the concave surface of reflection by theplane substantially perpendicular to the direction of the array of thelamp units, and a distance between both of cut faces is approximatelyhalf a diameter of an opening of the concave surface of reflection.Especially two lamp units arrayed in one direction have the quantity ofoutput light as much as about 1.5 times the conventional lighting devicewith a single lamp unit, while making the width of the lighting devicesubstantially the same. This arrangement enables the projector-typedisplay apparatus to utilize an optical system designed for a lamp unithaving a reflector with no side cuts.

In accordance with another preferable application, the reflectorsincluded in the plurality of lamp units are optically integrated withone another. This facilitates the manufacture of the lighting device.The term `optically integrated` means that the respective opticalelements are in close contact with one another. The plurality of opticalelements may be optically integrated by bonding them with an adhesive orby integrally forming them.

One preferable structure enables one of the light source lamps includedin the plurality of lamp units to be selectively turned on. Thisstructure enables the brightness of light to be adjusted in multiplesteps if required, thereby attaining the required brightness andefficient power consumption.

In accordance with another preferable structure, the light source lampsincluded in the plurality of lamp units emit respective light ofdifferent wavelength distribution characteristics. This structureenables the tint of light for illumination to be set to a predeterminedvalue, thereby improving the color reproducibility of a colorprojector-type display apparatus.

The lighting device preferably has an integrator optical system, inorder to reduce the unevenness of illuminance of light output from thelighting device. Namely the lighting device further includes anintegrator optical system having a first lens plate including aplurality of lenses and a second lens plate including a plurality oflenses, wherein the first lens plate spatially divides the light emittedfrom the light source lamp by the plurality of lenses included thereinto produce a plurality of intermediate light fluxes, which are focusedas secondary light source images in the vicinity of entrance planes ofthe plurality of lenses included in the second lens plate, output viathe plurality of lenses included in the second lens plate, andsuperposed on a predetermined illumination area. Even when there is asignificant variation of the intensity of light within a cross sectionof the light flux emitted from the lamp unit, the above structureenables the output light to be uniform in brightness and even in color.

In one preferable application of this structure, the lighting devicefurther includes polarizing means for converting light fluxes outputfrom the second lens plate to light fluxes of a single polarization typehaving identical polarizing directions and outputting the light fluxesof the single polarization type. The polarizing means has polarizationseparating means for separating the light fluxes output from the secondlens plate into light fluxes of two polarization types having differentpolarizing directions; and polarization converting means for convertingthe polarizing direction of one of the light fluxes of the twopolarization types obtained by the polarization separating means to thepolarizing direction of the other of the light fluxes of the twopolarization types, wherein the predetermined illumination area isilluminated with the polarized light fluxes of the single type havingidentical polarizing directions obtained by the polarizing means.

Since this structure uses only the light fluxes of a single polarizationtype having substantially identical polarizing directions forillumination, the utilization efficiency of light is improved when thelighting device is incorporated in, for example, a projector-typedisplay apparatus as discussed below. Light absorption hardly occurs inthe process of converting the light fluxes of random polarizingdirections to the polarized light fluxes of a single polarization typehaving substantially identical polarizing directions. This givesspecific polarized light fluxes with an extremely high efficiency.

The lighting device discussed above may be used as a light source of aprojector-type display apparatus. The projector-type display apparatusincludes the first lighting device of the present invention describedabove, modulation means for modulating light emitted from the lightingdevice responsive to image information, and a projection optical systemfor projecting a modulated light flux obtained by the modulation meansonto a projection plane. As described above, the first lighting deviceof the present invention ensures a greater quantity of output light,while having substantially the same size as that of the conventionallighting device. The projector-type display apparatus using the firstlighting device as the light source produces projection images of theimproved brightness, while having substantially the same size as that ofthe conventional apparatus with a single lamp unit.

In case that the lighting device has an integrator optical system, evenwhen there is a significant variation of the intensity of light within across section of the light flux emitted from the lamp unit, thisstructure enables the modulation means to be illuminated evenly with thelight of uniform brightness. The projector-type display apparatusaccordingly produces a projection image that is uniform in brightnessand even in color over the whole projection plane.

In accordance with one preferable application, the lighting deviceincludes the polarizing means having the polarization separating meansand the polarization converting means as described above. This structureenables the modulation means to be illuminated with light fluxes of asingle polarization type having identical polarizing directions.

In the projector-type display apparatus with the modulation meansutilizing light fluxes of a single polarization type, such as aliquid-crystal device, when the output light includes the light fluxesof random polarizing directions, polarization selecting means, such as apolarizing plate, is required to omit the polarized light fluxes of adifferent polarizing direction that is not used for the illumination.This extremely lowers the utilization efficiency of light. When thepolarizing plate is used as the polarization selecting means, a powerfulcooling device is required for cooling the polarizing plate, sinceabsorption of light significantly increases the temperature of thepolarizing plate. The above preferable structure, however, converts thelight fluxes of random polarizing directions emitted from the lightdevice to polarized light fluxes of a single polarization type havingsubstantially identical polarizing directions and enables the modulationmeans to be illuminated with the light fluxes of a single polarizationtype having substantially identical polarizing directions. Namely thisstructure utilizes most of the light fluxes emitted from the lightsource lamps and produces extremely bright projection images. The lightused for illumination and display includes little polarized light fluxesof a different polarizing direction, so that the amount of lightabsorbed by the polarizing plate is extremely small. This effectivelyprevents the temperature increase of the polarizing plate and remarkablyreduces the size of the cooling device for cooling the polarizing plate.

In order to project and display color images, the projector-type displayapparatus further includes color separation means for separating thelight emitted from the lighting device into at least two color lightfluxes; a plurality of the modulation means for modulating therespective color light fluxes separated by the color separation means;and color combining means for combining the color light fluxes modulatedby the plurality of modulation means, wherein a composite light fluxobtained by the color combining means is projected on the projectionplane via the projection optical system.

(Second Lighting Device and Projector-type Display Apparatus therewith)

The present invention is also directed to a second lighting device forilluminating an illumination area of a substantially rectangular shapehaving sides parallel to either of a first direction and a seconddirection which are substantially perpendicular to each other. Thesecond lighting device includes: a light source; a first lens platehaving a plurality of small lenses for dividing a light flux emittedfrom the light source into a plurality of partial light fluxes andcondensing the plurality of partial light fluxes; a second lens platehaving a plurality of small lenses on which the plurality of partiallight fluxes are incident; polarizing means comprising polarizationseparating means for separating each of the plurality of partial lightfluxes output from the second lens plate into light fluxes of twopolarization types having different polarizing directions, andpolarization converting means for converting the polarizing direction ofone of the light fluxes of the two polarization types obtained by thepolarization separating means to the polarizing direction of the otherof the light fluxes of the two polarization types, the polarizing meansthereby converting the plurality of partial light fluxes to plural lightfluxes of a single polarization type having substantially identicalpolarizing directions and outputting the plural light fluxes of thesingle polarization type; and superposing means for superposing theplural polarized light fluxes output from the polarizing means toilluminate the illumination area. The polarization separating means isarranged to cause the light fluxes of two polarization types to bespatially separated along the first direction of the illumination area.Each small lens of the first lens plate has a substantially rectangularshape when projected on a plane perpendicular to a central optical axisof the each small lens, wherein the substantially rectangular shape hasan aspect ratio that is virtually equal to an aspect ratio of theillumination area, and the plurality of partial light fluxes output fromthe small lenses are incident on corresponding small lenses of thesecond lens plate. Each small lens of the second lens plate has asubstantially rectangular shape when projected on a plane perpendicularto a central optical axis of the each small lens, wherein thesubstantially rectangular shape has an aspect ratio that is smaller thanthe aspect ratio of the illumination area. The aspect ratio is definedby a ratio of a length of the side parallel to the second direction to alength of the side parallel to the first direction.

Here the light flux passing through each small lens of the second lensplate is regarded as a set of illumination light flux. The attention isdrawn to the aspect ratio of the cross section of the illumination lightflux. In the second lighting device of the present invention, the secondlens plate includes the small lenses having the aspect ratio that issmaller than the aspect ratio of the small lenses of the first lensplate (which is virtually identical with the aspect ratio of theillumination area). The aspect ratio of the set of illumination lightflux is accordingly smaller than the aspect ratio of another set ofillumination light flux which would be obtained when the second lensplate had a plurality of small lenses having the aspect ratio that isidentical with the aspect ratio of the small lenses of the first lensplate. The cross section of the illumination light flux is accordinglyrectangular, wherein the length of the first direction is greater thanthe length of the second direction, corresponding to the aspect ratio ofthe small lenses of the second lens plate. (Among the sets ofillumination light fluxes passing through the second lens plate, theillumination light flux having the aspect ratio of its cross sectioncorresponding to the aspect ratio of the small lenses of the second lensplate is hereinafter referred to as the `compressed illumination lightflux`, whereas the illumination light flux having the aspect ratio ofits cross section corresponding to the aspect ratio of the small lensesof the first lens plate is hereinafter referred to as the`non-compressed illumination light flux`.)

When the lighting device of this structure is applied to aprojector-type display apparatus, a projection plane is illuminated withthe compressed illumination light fluxes via a projection lens. Comparedwith the non-compressed illumination light flux, the compressedillumination light flux has a smaller incident angle, at which the lightflux enters the projection lens, and enables a greater amount ofillumination light fluxes to enter on and in the vicinity of the centerof the lens pupil of the projection lens. The utilization efficiency oflight in a lens is generally higher at the position nearer to the centerof the lens pupil and worsens toward the periphery. Application of thesecond lighting device of the present invention to the projector-typedisplay apparatus enables the light emitted from the light source to beutilized efficiently and displays uniform and bright projection images.

The plurality of small lenses of the second lens plate, which have thesmaller aspect ratio than that of the small lenses of the first lensplate, are arranged to have substantially the same dimensions as thoseof a shape when projected on a plane perpendicular to the centraloptical axis of the second lens plate, which includes a plurality ofsmall lenses having the same aspect ratio as that of the small lenses ofthe first lens plate. The number of the small lenses of the second lensplate is identical with the number of the small lenses of the first lensplate. The reflector of the lamp unit is increased in size correspondingto the dimensions of a shape when projected on a plane perpendicular tothe central optical axis of the first lens plate. This increases theutilization efficiency of the light fluxes emitted from the light sourcelamp, without increasing the sectional dimensions of the optical systemexcept the reflector, compared with the conventional lighting devicewith the second lens plate which includes small lenses having the sameaspect ratio as that of the small lenses of the first lens plate.

In order to obtain the equivalent quantity of the compressedillumination light fluxes to that of the non-compressed illuminationlight fluxes, the optical elements in each optical system, which thelight output from the second lens plate passes through, have smallerrequired dimensions along the second direction. This desirably reducesthe size of the lighting device as well as the size of theprojector-type display apparatus with such a lighting deviceincorporated therein.

In accordance with one preferable application, the light source includesa plurality of lamp units arrayed in the second direction, each the lampunit having a light source lamp and a reflector for reflecting lightemitted from the light source lamp. Although requiring the additionalspace for the plurality of lamp units, the lighting device of thisstructure increases the quantity of output light.

When this lighting device is applied to the projector-type displayapparatus, the rays emitted from the plurality of lamp units aredeviated in a substantially symmetrical manner along the seconddirection with respect to the central optical axis of the second lensplate, when passing through the projection lens. As described above, theutilization efficiency of light in a lens is generally higher at theposition nearer to the center of the lens pupil and worsens toward theperiphery. As described in the prior art, the quantity of light outputfrom one lamp unit is extremely large in a central portion including anoptical axis of a light source lamp and abruptly decreases with adistance apart from the optical axis of the light source lamp. In thelighting device of the above structure, the width of the light outputfrom each lamp unit along the second direction is compressed about thecentral optical axis of the second lens plate. This enables the raysemitted from the plurality of lamp units to be led to the projectionlens with a high efficiency and realizes bright projection images.

The second lighting device of the present invention has the integratoroptical system including the first lens plate, the second lens plate,and the superposing means, thereby effectively reducing the unevennessof illuminance of light. The second lighting device also has thepolarizing means that generates light fluxes of s single polarizationtype having substantially identical polarizing directions as the lightof illumination. This structure utilizes most of the light fluxesemitted from the light source lamp and thereby improves the utilizationefficiency of light.

The plurality of partial light fluxes output from the first lens plateare focused in the vicinity of the second lens plate and thepolarization separating means to form secondary light source images. Thepolarization separating means divides each incident light flux along thefirst direction into two types of polarized light fluxes, so that twosecondary light source images are formed in alignment along the firstdirection on the polarization separating means. It is accordinglydesirable that the dimensions of the polarization separating means aresubstantially identical with or greater than the dimensions of the twosecondary light source images aligned along the first direction. Whenthe dimension along the first direction of each small lens included inthe second lens plate is substantially the same as the dimension alongthe first direction of the polarization separating means, the respectivesmalls lenses of the second lens plate and the polarization separatingmeans can be arranged at the highest efficiency without any clearances.The value of the aspect ratio of each small lens of the second lensplate may be set equal to approximately 1/2 by taking into account theefficiency of arrangement of the respective small lenses of the secondlens plate and the polarization separating means, when the secondarylight source images are approximated to have a substantially circularshape. This arrangement reduces the size of the second lens platewithout causing a light loss. This structure enables the light emittedfrom the light source to be efficiently utilized and obtains a largequantity of light for illumination.

In the lamp unit generally applied, the rays emitted from the lightsource lamp are reflected by the reflector and output as parallel rays.The parallelism of the output light from the lamp unit is worse at theposition closer to the lamp optical axis and improved with a distancefrom the lamp optical axis. The secondary light source images formed bythe plurality of partial light fluxes in the vicinity of the second lensplate and the polarization separating means are smaller at the positionfarther from the center of the second lens plate. It is accordinglypreferable that the plurality of small lenses of the second lens platearranged in a plurality of rows along the second direction are adjustedto have the dimension along the second direction that decreases withtheir distances from the center position of the light flux emitted fromthe light source.

This structure more efficiently decreases the width along the seconddirection of the set of illumination light flux passing through thesecond lens plate. This accordingly reduces the sizes of the second lensplate and the polarizing means and improves the utilization efficiencyof light output from the light source.

In the lighting device with the array of the plurality of lamp units,the reflector of each the lamp unit may have a shape obtained throughcutting a concave surface of reflection on at least one end adjoining toanother lamp unit by a plane substantially perpendicular to a directionof the array of the lamp units.

In a lamp unit with a reflector, the quantity of output light isextremely large in a central portion including an optical axis of alight source lamp and decreases with a distance from the optical axis ofthe light source lamp. In the lighting device of the above structure,the reflector of each lamp unit is cut to have a narrow width. Thisreduces the total width of the lighting device. This structure withnarrow reflectors effectively utilizes the output light in the centralportion including the lamp optical axis and thereby ensures a sufficientamount of output light. The lighting device of the present inventionensures a greater quantity of output light, while having substantiallythe same size as that of the conventional lighting device with only onelamp unit. The lighting device of the present invention is preferablyused as a light source of a projector-type display apparatus thatdisplays bright projection images.

The lighting device discussed above may be used as a light source of aprojector-type display apparatus. The projector-type display apparatusincludes the second lighting device of the present invention discussedabove, modulation means for modulating light emitted from the lightingdevice responsive to image information, and a projection optical systemfor projecting a modulated light flux obtained by the modulation meansonto a projection plane. As described above, the second lighting deviceof the present invention efficiently utilizes the light emitted from thelight source and obtains a large quantity of light for illumination. Theprojector-type display apparatus using the second lighting device as thelight source produces projection images of the improved brightness,while having substantially the same size as that of the conventionalapparatus with a single lamp unit.

The second lighting device of the present invention has the integratoroptical system as discussed above. Even when there is a significantvariation of the intensity of light within a cross section of the lightflux emitted from the lamp unit, this structure enables the modulationmeans to be illuminated evenly with the light of uniform brightness. Theprojector-type display apparatus accordingly produces a projection imagethat is uniform in brightness and even in color over the wholeprojection plane.

The second lighting device of the present invention has the polarizingmeans including the polarization separating means and the polarizationconverting means and enables the modulation means to be illuminated withlight fluxes of a single polarization type having substantiallyidentical polarizing directions. In the projector-type display apparatuswith the modulation means utilizing light fluxes of a singlepolarization type, such as a liquid-crystal device, this structureutilizes most of the light fluxes emitted from the light source lampsand produces extremely bright projection images. The light used forillumination and display includes little polarized light fluxes of adifferent polarizing direction, so that the amount of light absorbed bythe polarizing plate is extremely small. This effectively prevents thetemperature increase of the polarizing plate and remarkably reduces thesize of the cooling device for cooling the polarizing plate.

In order to project and display color images, the projector-type displayapparatus further includes color separation means for separating thelight emitted from the lighting device into at least two color lightfluxes; a plurality of the modulation means for modulating therespective color light fluxes separated by the color separation means;and color combining means for combining the color light fluxes modulatedby the plurality of modulation means, wherein a composite light fluxobtained by the color combining means is projected on the projectionplane via the projection optical system.

(Third and Fourth Projector-type Display Apparatuses)

The present invention is also directed to a third projector-type displayapparatus including: a lighting device having a plurality of lamp units,each the lamp unit including a light source lamp and a reflector forreflecting light emitted from the light source lamp; color separationmeans for separating light emitted from the lighting device into atleast two color light fluxes; and a plurality of modulation means formodulating the respective color light fluxes separated by the colorseparation means. The third projector-type display apparatus furtherincludes: color combining means for combining the color light fluxesmodulated by the plurality of modulation means; and a projection opticalsystem for projecting a composite light flux obtained by the colorcombining means onto a projection plane. When x, y, and z denote threedirectional axes perpendicular to one another and z represents adirection parallel to an optical axis of light emitted from the lampunit, the color separation means has a color separation plane that issubstantially perpendicular to an x-z plane and has predetermined angleswith respect to a y-z plane and an x-y plane, and the plurality of lampunits are arrayed substantially along the y direction.

The third projector-type display apparatus of the present invention thusconstructed requires the additional space for the plurality of lampunits, but effectively enhances the quantity of light emitted from thelighting device. Each lamp unit is arranged in a direction perpendicularto the light-dividing direction of a dichroic surface of the colorseparation means, so that the rays emitted from the respective lampunits enter the dichroic surface at an identical incident angle. Thisstructure effectively reduces color shift of each color light fluxoutput from the dichroic surface to the modulation means. Thisaccordingly enables an illumination area to be illuminated evenly withthe light of uniform brightness.

The present invention is further directed to a fourth projector-typedisplay apparatus including: a lighting device having a plurality oflamp units, each the lamp unit including a light source lamp and areflector for reflecting light emitted from the light source lamp; colorseparation means for separating light emitted from the lighting deviceinto at least two color light fluxes; and a plurality of modulationmeans for modulating the respective color light fluxes separated by thecolor separation means. The fourth projector-type display apparatusfurther includes: color combining means for combining the color lightfluxes modulated by the plurality of modulation means; and a projectionoptical system for projecting a composite light flux obtained by thecolor combining means onto a projection plane. When x, y, and z denotethree directional axes perpendicular to one another and z represents adirection parallel to an optical axis of light emitted from the lampunit, the color combining means has a dichroic surface that is arrangedto be substantially perpendicular to an x-z plane and have predeterminedangles with respect to a y-z plane and an x-y plane, and the pluralityof lamp units are arrayed substantially along the y direction.

Like the third projector-type display apparatus, the fourthprojector-type display apparatus of the present invention thusconstructed requires the additional space for the plurality of lampunits, but effectively enhances the quantity of light emitted from thelighting device. Each lamp unit is arranged in a direction perpendicularto the light-dividing direction of the dichroic surface of the colorcombining means, so that the rays emitted from the respective lamp unitsenter the dichroic surface at an identical incident angle. Thisstructure effectively reduces color shift of the composite light fluxoutput from the dichroic surface to the projection optical system. Thisaccordingly produces a projection image of uniform brightness and evencolor.

In the third and the fourth projector-type display apparatuses of thepresent invention, the reflector of each the lamp unit may have a shapeobtained through cutting a concave surface of reflection on at least oneend adjoining to another lamp unit by a plane substantiallyperpendicular to a direction of the array of the lamp units. Thereflectors of this arrangement decrease the area occupied by the lampunits and thereby reduce the size of the projector-type displayapparatus. These reflectors enable the rays in central portionsincluding lamp optical axes to be effectively utilized and ensure thesufficient quantity of output light. This accordingly enables uniformand bright projection images to be projected and displayed.

In order to eliminate the unevenness of illuminance of light in thethird and the fourth projector-type display apparatuses of the presentinvention, it is desirable that the lighting device has an integratoroptical system. In a preferable structure, the lighting device has anintegrator optical system including a first lens plate with a pluralityof lenses and a second lens plate with a plurality of lenses. Even whenthere is a significant variation of the intensity of light within across section of the light flux emitted from the lamp unit, thisstructure gives the light of uniform brightness and even color. Theprojector-type display apparatus accordingly produces a projection imagethat is uniform in brightness and even in color over the wholeprojection plane.

In accordance with one preferable application, the lighting device haspolarizing means for converting light fluxes output from the second lensplate to light fluxes of a single polarization type having identicalpolarizing directions. The illumination area is then illuminated withlight fluxes of the single polarization type having identical polarizingdirections, which are obtained by the polarizing means. This structureutilizes most of the light fluxes emitted from the light source lampsand produces extremely bright projection images. The light used forillumination and display includes little polarized light fluxes of adifferent polarizing direction, so that the amount of light absorbed bythe polarizing plate is extremely small. This effectively prevents thetemperature increase of the polarizing plate and remarkably reduces thesize of the cooling device for cooling the polarizing plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an optical system of a lighting deviceas a first embodiment according to the present invention;

FIG. 2 is a perspective view schematically illustrating a light sourceunit included in the lighting device of FIG. 1;

FIG. 3 shows a contour of the light source unit of FIG. 1 seen from thedirection of lamp optical axes;

FIG. 4 shows a distribution of the quantity of light output from eachlamp unit of the light source unit of FIG. 1 in the directionperpendicular to the lamp optical axis;

FIG. 5 is a perspective view schematically illustrating structure of afirst lens plate included in the integrator optical system of FIG. 1;

FIGS. 6(A), 6(B), and 6(C) show wavelength distribution characteristicsof light emitted from the lighting device of FIG. 1;

FIG. 7 shows available lighting modes in the lighting device of FIG. 1;

FIG. 8 schematically illustrates an optical system of a lighting deviceas a second embodiment according to the present invention;

FIG. 9 is a perspective view illustrating the shielding plate of FIG. 8;

FIG. 10 is a perspective view illustrating the array of polarizationseparating units of FIG. 8;

FIG. 11 shows structure and function of each polarization separatingunit included in the array of polarization separating units of FIG. 8;

FIG. 12 schematically illustrates an essential part of an optical systemof a projector-type display apparatus as a third embodiment according tothe present invention;

FIGS. 13(A) and 13(B) schematically illustrate an optical system of alighting device as a fourth embodiment according to the presentinvention;

FIGS. 14(A), 14(B), and 14(C) shows converged images of a light sourceformed by the flux division lenses and the condenser lenses of FIG. 13;

FIGS. 15(A) and 15(B) illustrate a structure of the flux division lensesand the condenser lenses of FIG. 13;

FIG. 16 shows the positional relationship between the flux divisionlenses and the condenser lenses of FIG. 13 in the y direction;

FIGS. 17(A), 17(B), and 17(C) show incident rays entering a projectionlens when the lighting device of FIG. 13 is applied to a projector-typedisplay apparatus;

FIG. 18 shows another structure of the condenser lens array of FIG. 13;

FIG. 19 shows converged images formed by a plurality of intermediatelight fluxes in the vicinity of the condenser lens array of FIG. 13;

FIGS 20(A) and 20(B) show the positional relationship between dichroicmirrors and lamp units arrayed in the y-axis direction;

FIG. 21 shows the positional relationship between dichroic mirrors andlamp units arrayed in the x-axis direction; and

FIG. 22 is a graph showing color separation characteristics of ablue-green light reflection dichroic mirror.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention are discussed below withreference to the drawings. In the following description of theembodiments, for the matter of convenience, three directionsperpendicular to one another are defined as an x-axis direction (lateraldirection), a y-axis direction (vertical direction), and a z-axisdirection (direction parallel to the optical axis), unless otherwisespecified.

(First Embodiment)

FIG. 1 schematically illustrates an essential part of a lighting deviceembodying the present invention. A lighting device 1 of the embodimentbasically includes a light source unit 2 and an integrator opticalsystem 3, which are arranged along a system optical axis 1L (the z-axisdirection). A light beam emitted from the light source unit 2 passesthrough the integrator optical system 3 and reaches an illumination area4 as a uniform ray of even illuminance. The integrator optical system 3includes a first lens plate 31, a second lens plate 32, and a field lens(superposing lens) 33.

The light source unit 2 has a first lamp unit 21A and a second lamp unit21B having an identical structure and identical dimensions. These lampunits 21A and 21B are arranged to have lamp optical axes 21L in parallelto the system optical axis 1L and to be in parallel in a directionsubstantially perpendicular to their lamp optical axes 21L, that is, inthe x-axis direction.

FIG. 2 is a perspective view illustrating the pair of lamp units 21included in the light source unit 2. The lamp units 21A and 21Brespectively have light source lamps 210A and 210B and reflectors 220Aand 220B, for example, in the shape of paraboloid. FIG. 3 illustrates acontour of the reflectors 220 when the pair of lamp units 21A and 21Bare seen from the side of the integrator optical system 3. Eachreflector 220A or 220B is a concave body of a paraboloidal shape withboth sides cut off, which is symmetrical about the lamp optical axis21L. Namely each reflector 220A or 220B having a width of 1/2 W isobtained by cutting off both side portions of a concave body 230A or230B, which has a circumferential opening as shown by the broken line,substantially along the y axis by a width of approximately one quarter adiameter W The lamp units 21A and 21B including the reflectors 220A and220B with the both sides cut off (hereinafter may be referred to asside-cut lamp units) are arranged in parallel in the directionperpendicular to the lamp optical axes 21L (that is, in the x-axisdirection) and connected to each other. The total width of these lampunits 21A and 21B (the width in the x-axis direction) is equal to thewidth W of one reflector with no side cuts.

FIG. 4 shows a quantity-of-light distribution curve C in the directionperpendicular to the lamp optical axis 21L in the lamp unit 21 with theparaboloidal reflector. As understood from this graph, the quantity ofoutput light is extremely large in a central portion including the lampoptical axis 21L and abruptly decreases with an increase in distancefrom the lamp optical axis 21L. Like the lamp units 21A and 21B of theembodiment, the reflector 220A or 220B obtained by cutting off both sideportions by the total width of approximately 1/2 W can utilize most ofthe quantity of the output light. The lighting device 1 of theembodiment accordingly increases the brightness of the illumination areato or above approximately 1.5 times the brightness of the conventionalstructure with a single lamp unit.

Referring back to FIG. 1, the light beam output from the light sourceunit 2 enters the first lens plate 31 of the integrator optical system3. FIG. 5 illustrates the first lens plate 31. As shown in FIG. 5, thefirst lens plate 31 includes a plurality of small rectangular lenses(lenses having a rectangular outer shape in an x-y plane) 311 arrangedin a matrix. The outer shape of the rectangular lenses 311 on the x-yplane is set similar to the shape of the illumination area 4. The secondlens plate 32 shown in FIG. 1 consists of the same number of smalllenses 321 as that of the rectangular lenses constituting the first lensplate 31.

The light beam entering the first lens plate 31 is spatially divided bythe respective rectangular lenses 311 to form secondary light-sourceimages inside the respective rectangular lenses 321 of the second lensplate 32. Namely the focal position of each rectangular lens 311 isinside and near to the corresponding rectangular lens 321.

The plurality of secondary light-source images formed on the second lensplate 32 are superposed one upon another and focused on the illuminationarea 4 via the field lens 33 attached to the output side of the secondlens plate 32, so as to illuminate the illumination area 4 substantiallyuniformly. In principle, all the flux of output light from the lightsource unit 2 thus enters the illumination area 4. The structure may notrequire the field lens 33 when the small lenses 321 constituting thesecond lens plate 32 are decentered lenses having the function ofsuperposing the rays on the illumination area.

As discussed above, the lighting device 1 of the embodiment includes thelight source unit 2 of the structure in which the lamp units 21A and 21Bhaving the paraboloidal reflectors with both sides cut off are arrangedin parallel. The width of the lighting device 1 is accordingly identicalwith the width of the conventional lighting device having a single lampunit. The lighting device 1 utilizes the output light in a centralportion including the lamp optical axes, which occupies most of thequantity of output light of the lamp units 21A and 21B. Although bothsides of the reflectors are cut off, the lighting device 1 secures about1.5 times as much quantity of light as a conventional device with asingle lamp unit. Compared with a lamp unit without any side cuts, thelamp units 21A and 21B having the side-cut reflectors have bettercooling efficiency and less temperature increase.

As described before, a light source lamp of a short arc length used asthe lamp unit improves the parallelism of the output rays, but causes adistribution of the quantity of output light which is extremely large inthe portion of the lamp optical axis and abruptly decreases towards theperipheral portion. When the light beam emitted from such a lamp unitenters the lens plate included in the integrator optical system, unevenbrightness is prominent; that is, the peripheral area is remarkablydarker than the central area of the lens plate. In case that the size ofone small lens (rectangular lens) is larger, uneven brightness would bealso prominent in the flux of light passing through the respective smalllenses of the first lens plate 31. In order to obtain the rays ofuniform brightness, it is required to increase the number of lensdivisions of the lens plate and reduce the size of each small lens. Thelighting device 1 of the embodiment including the light source unit andthe integrator optical system, on the other hand, utilizes the outputrays having the large quantity of light in the central portions of thetwo side-cut lamp units. This structure reduces the difference inbrightness between the central area and the peripheral area. Thestructure of the embodiment accordingly enables the illumination area tobe illuminated evenly with uniform brightness, without increasing thenumber of lens divisions of the lens plate included in the integratoroptical system.

In the embodiment, the width of each lamp unit is approximately 1/2 W.The width is, however, not restricted to 1/2 W but may be, for example,7/10 W through 3/10 W. The width of each lamp unit, or the cut-off widthof each reflector, should be set appropriately according to thedistribution of the quantity of light output from the lamp unitsapplied.

The pair of lamp units may have different widths, and the cut-off widthson both sides of the reflector may be different in each lamp unit.Especially when the integrator optical system is provided like thisembodiment, combination of the lamp units having different widths moreeffectively reduces the unevenness of illuminance on the illuminationarea. In the structure of the embodiment, the light source unitincluding the pair of lamp units having an identical width is arrangedto have its center coinciding with the system optical axis. In thecombination of lamp units having different widths, however, the systemoptical axis is deviated from the center of the lamp optical axis ofeach lamp unit. This structure of the lamp units causing anunsymmetrical distribution of intensity of light output from the lightsource unit with respect to the system optical axis effectively reducesthe unevenness of illuminance on the illumination area. This modifiedstructure does not require the center of the light source unit tocoincide with the system optical axis and thereby increases the degreeof freedom in the layout of the constituents.

In this embodiment, both side portions of each reflector in the x-axisdirection are cut off to narrow the width and the lamp units arearranged in the x-axis direction. In another preferable structure, bothside portions of each reflector in the y-axis direction may be cut offto narrow the width and the lamp units are arranged in the y-axisdirection.

Although the pair of lamp units are arranged in parallel in theembodiment, three or more lamp units may be arranged in parallel or inseries. For example, four lamp units having narrow reflectors with sideportions cut off in both the x-axis direction and in the y-axisdirection may be arranged in a 2×2 matrix to construct a light sourceunit. This modified structure has substantially the same size as aconventional device with a single lamp unit, to provide a remarkablybrighter light source.

The light source unit may be constructed to be an array of plural lampunits, each having one reflector and one light source lamp. In anotherpossible structure , a plurality of light source lamps are arrayed in aplurality of reflectors integrally formed in advance. Compared with theformer structure, the latter structure is readily manufactured andenables the thickness of the boundary between the adjoining reflectorsto be reduced. The latter structure accordingly reduces themanufacturing cost, the size of the light source unit, and the lightloss on the boundary between the adjoining reflectors. The section ofthe reflector may have an ellipsoidal or circular shape other than theparaboloidal shape. In other words, a reflector may have a shape whichis prepared by cutting a concave surface of revolution, obtained byrotating a curve (especially a quadric curve) about the optical axis ofa light source lamp, on at least one end adjoining to another lamp unitby a plane substantially perpendicular to the direction of the array ofthe lamp units.

Although the lamp unit of this embodiment includes the same type oflight source lamps, it may include light source lamps of differentspectra; such a lamp unit can improve color reproducibility of a colorprojector-type display apparatus. FIG. 6 shows wavelength distributioncharacteristics of light in the lighting device 1. The wavelengthdistribution characteristics (spectral characteristics) of the lightingdevice generally depend upon the type of the light source lamp usedtherein. For example, some light source lamps give outputs over thewhole range of visible rays but have insufficient outputs in the redlight range. It is assumed here that the desirable spectroscopicdistribution characteristics of the lighting device 1 show substantiallyequal relative outputs over the wavelength range for respective colorrays as shown in FIG. 6(C). The wavelength distribution of the lamp unit21A (light source lamp 210A) is characterized by low relative outputs inthe red light range as shown in FIG. 6(A). In this case, the lightsource lamp 210B should be selected to enable the wavelengthdistribution of the lamp unit 21B to have high relative outputs in thered light range as shown in FIG. 6(B). The rays output from the wholelighting device 1 substantially equal to the sum of the outputs of thelamp units 21A and 21B and the desired wavelength distributioncharacteristics can be obtained as shown in FIG. 6(C). Some combinationsof lamp units give rays of strong red tint or those of strong blue tint.Combining the light characteristics of two lamp units results in rays ofvarious characteristics. The wave length distribution shown in FIG. 6 isonly an example for illustrating the effects of this embodiment, butlight source lamps having a variety of other wavelength distributioncharacteristics are applicable as well.

Another advantage of the embodiment including two lamp units is to allowcontinuous operation with lowered illuminance even when one lamp hasburnt out during operation.

A control circuit 10 (see FIG. 1) may selectively turn on and off thetwo light source lamps. This enables the brightness of light to beadjusted in multiple steps according to the requirements, therebyattaining the required brightness and efficient power consumption. FIG.7 shows available lighting modes of the lighting device 1. As describedabove, the lighting device 1 includes the two light sources, the lampunits 21A and 21B, so that there are four lighting modes: mode 0 throughmode 3 shown in FIG. 7. In the mode 0, both the lamp units 21A and 21are turned off. In the mode 1, the lamp unit 21A is turned on, while thelamp unit 21B is turned off. In the mode 2, the lamp unit 21A is turnedoff, while the lamp unit 21B is turned on. In the mode 3, both the lampunits 21A and 21B are turned on. The lighting mode is switched by anon-illustrated switching circuit. Selection of an appropriate modeexerts the effects discussed below.

Selection of the mode 3 enables the illumination area 4 to beilluminated with light output from both the lamp units 21A and 21B, andthus gives light of large intensity. This enhances the intensity oflight as well as the utilization efficiency of light without requiringextremely high-output light source lamps for the light source lamps 210Aand 210B of the lamp units 21A and 21B.

In the normal operating state, either the mode 1 or the mode 2 isselected, and the illumination area 4 is illuminated with light outputfrom either one of the lamp units 21A and 21B. For example, the mode 1is selected in the normal operating state to turn only the lamp unit 21Aon for illumination of the illumination area 4. When the lamp unit 21Amalfunctions or the light source lamp 210A burns out, the mode 2 isselected to turn on the light source lamp 210B of the lamp unit 21B forthe continuous operation. This improves the life of the lighting opticalsystem.

Further, the light source lamps 210A and 210B may have differentluminance. For example, the light source lamp 210A of the lamp unit 21Ais set to have a luminance in the normal operating state, whereas thelight source lamp 210B of the lamp unit 21B is set to have a lowerluminance. This changes the intensity of light in three different steps.Selection of the mode 1 gives light of a normal intensity. Selection ofthe mode 3 gives light of a greater intensity, whereas selection of themode 2 gives light of a smaller intensity.

(Second Embodiment)

FIG. 8 schematically illustrates an essential part of a polarizinglighting device embodying the present invention. A polarizing lightingdevice 60 of this embodiment includes a light source unit 2 having anidentical structure to that of the light source unit 2 of the lightingdevice 1 described above. The polarizing lighting device 60 alsoincludes an integrator optical system having two lens plates, that is, afirst optical element 71 and a condenser lens array 720. The firstoptical element 71, the condenser lens array 720, and a superposing lens760 have substantially the same functions as those of the first lensplate 31, the second lens plate 32, and the filed lens 33 shown inFIG. 1. The difference is that a polarizing optical system is arrangedbetween the condenser lens array 720 and the superposing lens 760 forconverting the light output from the light source unit 2 to polarizedlight having one polarizing direction.

The polarizing lighting device 60 of the embodiment basically includesthe light source unit 2 and a polarizing unit 7 having the function ofthe integrator optical system, which are arranged along a system opticalaxis 60L. The light flux of random polarizing directions emitted fromthe light source unit 2 (hereinafter referred to as the light flux ofrandom polarization) is converted by the polarizing unit 7 to a lightflux of substantially identical polarizing directions, which thenreaches the illumination area 4. The light source unit 2 is arranged insuch a manner that an optical axis R of the light emitted from the lightsource unit 2 is a parallel displacement of the system optical axis 60Lin the x-axis direction of by a predetermined distance D.

The polarizing unit 7 includes the first optical element 71 and a secondoptical element 72. The positional relationship between the light sourceunit 2 and the first optical element 71 is specified to make the opticalaxis R of the light source unit 2 coincident with the center of thefirst optical element 71. The light entering the first optical element71 is divided by an array of flux division lenses 711 into a pluralityof intermediate light fluxes 712, which are focused by thebeam-condensing function of the flux division lenses to form the samenumber of converged images (secondary light-source images) 713 as thenumber of the flux division lenses in a plane perpendicular to thesystem optical axis 60L (an x-y plane in FIG. 8). The outer shape of thearray of the flux division lenses 711 on the x-y plane is set similar tothe shape of the illumination area 4. In this embodiment, there is awide illumination area wider in the x direction on the x-y plane, sothat the flux division lenses 711 have a wide outer shape on the x-yplane.

The second optical element 72 is a complex essentially including thecondenser lens array 720, a shielding plate 730, an array ofpolarization separating units 740, a selective phase difference plate750, and the superposing lens 760. The second optical element 72 thusconstructed is arranged in the plane perpendicular to the system opticalaxis 60L (the x-y plane) and in the vicinity of the position of theconverged images 713 formed by the first optical element 71. The secondoptical element 72 spatially separates each of the intermediate lightfluxes 712 to a p-polarized light flux and an s-polarized light flux,adjusts these fluxes to either one of the polarizing directions, andleads the fluxes of substantially identical polarizing directions to theillumination area 4.

The condenser lens array 720 has the function of condensing and leadingthe respective intermediate light fluxes to specific positions of thearray of polarization separating units 740. It is desirable that thelens characteristics of each condenser lens 721 are optimized by takinginto account the fact that it is ideal that the slope of the primaryrays entering the array of polarization separating units 740 is parallelto the system optical axis 60L.

In general, however, for the cost reduction of the optical system andthe readiness of design, the structure identical with the first opticalelement 71 may be applied for the condenser lens array 720. In anotherexample, the condenser lens array may consist of condenser lenses havingthe similar outer shape to that of the flux division lenses 711 in thex-y plane. In this embodiment, the structure identical with the firstoptical element 71 is applied for the condenser lens array 720. Thecondenser lens array 720 may be arranged apart from the shielding plate730 and the array of polarization separating units 740 (that is, near tothe first optical element 71).

FIG. 9 is a perspective view illustrating the appearance of theshielding plate 730. As shown in FIG. 9, the shielding plate 730includes a plurality of shielding surfaces 731 and a plurality ofopening surfaces 732 arranged in a matrix. The arrangement of theshielding surfaces 731 and the opening surfaces 732 corresponds to thearrangement of the array of polarization separating units 740 discussedlater. The light fluxes entering the shielding surfaces 731 of theshielding plate 730 are blocked, whereas the light fluxes entering theopening surfaces 732 are allowed to pass through the shielding plate730. The shielding plate 730 accordingly has the function of controllingthe transmission of light fluxes according to the position on theshielding plate 730. The arrangement of the shielding surfaces 731 andthe opening surfaces 732 is specified to cause the converged images 713by the first optical element 71 to be formed only on polarizationseparating surfaces 741 of the array of polarization separating units740 as discussed later. In this embodiment, the shielding plate 730 is atransparent flat plate (for example, a glass plate) partly covered witha light-shielding film (for example, a chromium film, an aluminum film,or a dielectric multi-layered film). In another example, the shieldingplate 730 may be a light-shielding flat plate, such as an aluminumplate, with openings. In case that the light-shielding film is appliedfor the shielding surfaces, the light-shielding film may be formeddirectly on the condenser lens array 720 or the array of polarizationseparating units 740 discussed later.

FIG. 10 is a perspective view illustrating the appearance of the arrayof polarization separating units 740. As shown in FIG. 10, the array ofpolarization separating units 740 includes a plurality of polarizationseparating units 770 arranged in a matrix. The arrangement of thepolarization separating units 770 corresponds to the lenscharacteristics and the arrangement of the flux division lenses 711 ofthe first optical element 71. In this embodiment, the concentric fluxdivision lenses 711 having an identical shape are arranged in anorthogonal matrix to constitute the first optical element 71. Thepolarization separating units 770 having an identical shape are thusarrayed in a fixed direction and arranged in an orthogonal matrix toconstitute the array of polarization separating units 740. When all thepolarization separating units aligned in the same row in the y directionhave an identical shape, a plurality of long polarization separatingunits that have the longitudinal axis in the y direction and a height Hidentical with the height of the array of polarization separating units740 may be arrayed in the x direction and combined with one another toconstruct the array of polarization separating units. This structureimproves the degree of flatness of an interface in the x directionbetween the adjacent long polarization separating units. Suchconstruction accordingly lowers the light loss in the interface betweenthe adjacent polarization separating units and reduces the manufacturingcost for the array of polarization separating units.

In this embodiment, the array of polarization separating units 740 isdescribed as a complex of the plurality of polarization separating units770. The concept of the basic structural units, that is, thepolarization separating units, is, however, only used to explain thefunction of the array of polarization separating units. Namely the arrayof polarization separating units 740 may be formed integrally, insteadof as a complex of the basic structural units or the polarizationseparating units. This modified structure is free of the light loss inthe interface between the adjacent polarization separating units.

FIG. 11 illustrates the appearance and function of each polarizationseparating unit 770. As shown in FIG. 11, the polarization separatingunit 770 is a quadratic prism including a polarization separatingsurface 741 and a reflection surface 742, and has the function ofspatially separating each of the intermediate light fluxes entering thepolarization separating unit into a p-polarized light flux and ans-polarized light flux. The outer shape of the polarization separatingunit 770 on the x-y plane is similar to the outer shape of the fluxdivision lens 711 on the x-y plane; that is, a wide rectangular shape.The polarization separating surface 741 and the reflection surface 742are aligned in the longitudinal direction of the contour of thepolarization separating unit 770, that is, in the lateral direction (xdirection). The polarization separating surface 741 is arranged to havea slope of approximately 45 degrees to the system optical axis L,whereas the reflection surface 742 is parallel to the polarizationseparating surface 741. The area of projection of the polarizationseparating surface 741 on the x-y plane (that is identical with the areaof a p-output plane 743 discussed later) is equal to the area ofprojection of the reflection surface 742 on the x-y plane (that isidentical with the area of an s-output plane 744 discussed later). Inthis embodiment, a width Wp of the area on the x-y plane where thepolarization separating surface 741 exists is equal to a width Wm of thearea on the x-y plane where the reflection surface 742 exists. Both thewidths Wp and Wm are half a width WI of the polarization separating uniton the x-y plane. The polarization separating surface 741 is generallycomposed of a dielectric multi-layered film, whereas the reflectionsurface 742 is composed of either a dielectric multi-layered film or analuminum film.

The light entering the polarization separating unit 770 is separated bythe polarization separating surface 741 into a p-polarized light flux745, which does not change the course and passes through thepolarization separating surface 741, and an s-polarized light flux 746,which is reflected by the polarization separating surface 741 andchanges the course toward the adjoining reflection surface 742. Thep-polarized light flux 745 reaches the p-output plane 743 and is outputfrom the polarization separating unit 770. The s-polarized light flux746 changes the course again on the reflection surface 742 to besubstantially parallel to the p-polarized light flux 745, reaches thes-output plane 744, and is eventually output from the polarizationseparating unit 770. The polarization separating unit 770 separates theincident light flux of random polarization into the p-polarized lightflux 745 and the s-polarized light flux 746, which have differentpolarizing directions but are output in a substantially identicaldirection from the different places of the polarization separating unit770 (that is, the p-output plane 743 and the s-output plane 744).

It is required to lead the intermediate light flux 712 (see FIG. 8)entering each polarization separating unit 770 to the area where thepolarization separating surface 741 exists. The positional relationshipbetween the respective polarization separating units 770 and therespective condenser lenses 721 and the lens characteristics of therespective condenser lenses 721 are specified to enable the intermediatelight flux 712 to form a secondary light-source image in the vicinity ofthe central portion of each polarization separating surface 741. In thisembodiment, each condenser lens is arranged to position its central axisin the central portion of the polarization separating surface 741included in each polarization separating unit 770. The condenser lensarray 720 is accordingly shifted in the x direction from the array ofpolarization separating units 740 by the distance D (see FIG. 8), whichcorresponds to one quarter of the width WI of each polarizationseparating unit.

Referring back to FIG. 8, the shielding plate 730 is interposed betweenthe array of polarization separating units 740 and the condenser lensarray 720. The centers of the respective opening surfaces 732 in theshielding plate 730 are arranged to substantially coincide with thecenters of the polarization separating surfaces 741 of the respectivepolarization separating units 770. The opening width of each openingsurface 732 (that is, the opening width in the x direction) is set to beapproximately half the width WI of the polarization separating unit 770.There exist substantially no intermediate light fluxes that directlyenter the reflection surfaces 742 but not via the polarizationseparating surfaces 741, since such intermediate light fluxes have beenblocked by the shielding surfaces 731 of the shielding plate 730. Almostall the light fluxes passing through the opening surfaces 732 of theshielding plate 730 enter only the polarization separating surfaces 741.Because of the presence of the shielding plate 730, there existsubstantially no light fluxes that directly enter the reflectionsurfaces 742 and then go to the adjoining polarization separatingsurfaces 741 in the polarization separating units.

The selective phase difference plate 750 including λ/2 phase differenceplates 751 arranged in a regular manner is placed on the side of theoutput planes of the array of polarization separating units 740. Moreconcretely, the λ/2 phase difference plates 751 are placed correspondingto the p-output planes 743 (see FIG. 11) of the respective polarizationseparating units 770, whereas no λ/2 phase difference plates 751 areplaced corresponding to the s-output planes 744. Such arrangement of theλ/2 phase difference plates 751 causes the p-polarized light flux outputfrom the polarization separating unit 770 to be subjected to a rotationin the polarizing direction in the course of passing through the λ/2phase difference plate 751 and to be converted to the s-polarized lightflux. The s-polarized light flux output from the s-output plane 744, onthe other hand, does not enter the λ/2 phase difference plate 751, butpasses through the selective phase difference plate 750 with thepolarizing direction unchanged. Namely the array of polarizationseparating units 740 and the selective phase difference plate 750convert the intermediate light fluxes of random polarizing directions tothe light fluxes of identical polarizing direction (the s-polarizedlight fluxes in this case). The superposing lens 760 is placed on theside of the output plane of the selective phase difference plate 750.The light fluxes adjusted to the s-polarized light fluxes by thefunction of the selective phase difference plate 750 are led by thesuperposing lens 760 to the illumination area 4 and superposed thereon.The superposing lens 760 may not be one independent lens body but acomplex of a plurality of lenses like the first optical element 71.

In summary, the second optical element 72 has the following functions.The intermediate light fluxes 712 divided by the first optical element71 (which fluxes represent image planes cut by the flux division lenses711) are superposed on the illumination area 4 by the function of thesecond optical element 72. The array of polarization separating units740 spatially separate the intermediate light fluxes of randompolarization into two different polarized light fluxes having differentpolarizing directions. The selective phase difference plate 750 thenconverts these polarized light fluxes to the light fluxes ofsubstantially identical polarizing directions. The shielding plate 730is placed on the side of the entrance planes faces of the array ofpolarization separating units 740, in order to cause the intermediatelight fluxes to enter only the polarization separating surfaces 741included in the polarization separating units 770. There accordinglyexist substantially no intermediate light fluxes that enter thereflection surfaces 742 and the polarization separating surfaces 741 inthis order. The polarized light fluxes output from the polarizationseparating units 770 are thus restricted to substantially one type. Thismeans that the illumination area 4 is uniformly illuminated with thelight fluxes of substantially identical polarizing directions.

As discussed above, the size of the converged images 712 formed by thefirst optical element 71 is affected by the parallelism of the lightfluxes entering the first optical element 71 (the light fluxes emittedfrom the light source in the case of the lighting device). The poorparallelism results in converged images of large dimensions. In such acase, there exist many intermediate light fluxes that directly enter thereflection surfaces but not via the polarization separating surfaces inthe polarization separating units. This causes the polarized lightfluxes having different polarizing directions to be undesirably mixedwith each other for illumination. The polarizing lighting device of FIG.8 has the shielding plate 730, which is especially effective when thelight source in the polarizing lighting device emits the light fluxes ofpoor parallelism.

When most of the intermediate light fluxes directly enter thepolarization separating surfaces 741 (that is, little intermediate lightfluxes directly enter the reflection surfaces 742), the shielding plate730 can be omitted. The condenser lens array 720 may also be omittedwhen the light fluxes output from the light source unit have highparallelism.

As described above, the polarizing lighting device 60 of the embodimentexerts the similar effects to those of the lighting device 1 as well asthe additional effects described below. The polarizing unit 7 includingthe first optical element 71 and the second optical element 72 convertsthe light fluxes of random polarization emitted from the light sourceunit 2 to the light fluxes of substantially identical polarizingdirections, and enables the illumination area 4 to be illuminateduniformly with the light fluxes of substantially identical polarizingdirections. This structure is virtually free of the light loss in thecourse of generating the polarized light fluxes, so that almost all thelight fluxes emitted from the light source unit can be led to theillumination area 4. This attains an extremely high utilizationefficiency of light. The shielding plate 730 included in the secondoptical element 72 effectively prevents the light fluxes of differentpolarizing directions from being mixed with each other for illuminatingthe illumination area 4. When the polarizing lighting device of thepresent invention is used to illuminate a modulation means for carryingout a display with polarized light fluxes, such as a liquid crystaldevice, a polarizing plate conventionally placed on the light-entranceside of the modulation means may be omitted. Even when the polarizingplate is required, an extremely little quantity of light absorption inthe polarizing plate remarkably reduces the size of a cooling devicerequired for preventing a temperature increase of the polarizing plateand the modulation means.

In this embodiment, the condenser lens array 720, the shielding plate730, the array of polarization separating units 740, the selective phasedifference plate 750, and the superposing lens 760, which are all theconstituents of the second optical element 72, are optically integratedwith one another. Such arrangement reduces the light loss in therespective interfaces and further enhances the utilization efficiency oflight. The term `optically integrated` implies that the respectiveoptical elements are in close contact with one another. The plurality ofoptical elements are optically integrated by bonding them with anadhesive or by integrally forming them.

The flux division lenses 711 of the first optical element 71 are of awide shape corresponding to the wide rectangular shape of theillumination area 4, and separate the two different polarized lightfluxes output from the array of polarization separating units 740 in thelateral direction (x direction). The structure of the embodiment doesnot waste the quantity of light but enables the illumination area 4 ofthe wide rectangular shape to be illuminated with a high efficiency(utilization efficiency of light).

When the light fluxes of random polarizing directions are simplyseparated into the p-polarized light fluxes and the s-polarized lightfluxes, the total width of the light fluxes after the separation isdoubled and makes the optical system undesirably bulky. In thepolarizing lighting device of the present invention, the first opticalelement 71 functions to form the plurality of small converged images713, while the reflection surfaces 742 are disposed in the space whereno converged images 713 exist. This arrangement absorbs the extension ofthe optical path in the lateral direction due to the separation into twodifferent polarized light fluxes and effectively prevents an increase intotal width of the light fluxes, thereby reducing the size of theoptical system.

(Third Embodiment)

The following describes a projector-type display apparatus with apolarizing lighting device 60A incorporated therein, which basically hasthe identical structure to that of the lighting device 60 describedabove. In this embodiment, a transmission liquid-crystal device is usedas a modulation means for modulating light fluxes output from thepolarizing lighting device responsive to display information.

FIG. 12 schematically illustrates the x-y plane structure of anessential part of an optical system included in a projector-type displayapparatus 80 embodying the present invention. The projector-type displayapparatus 80 of the embodiment essentially includes the polarizinglighting device 60A, a color separation optical system 400 forseparating a white color light flux into three color rays, threetransmission liquid-crystal devices 411, 412, and 413 for modulating therespective color rays responsive to display information to generatedisplay images, a cross dichroic prism 450 functioning as a colorcombining means for combining the three color rays to create a colorimage, and a projection lens 460 functioning as a projection opticalsystem for projecting and displaying the color image.

The polarizing lighting device 60A includes a light source unit 2 havinga pair of lamp units 2 1A and 2 1B for emitting light fluxes of randompolarization in one direction. The light fluxes of random polarizationemitted from the light source unit 2 are converted by a polarizing unit7 to light fluxes of substantially identical polarizing directions. Inthe polarizing lighting device 60A of the embodiment, a first opticalelement 71 and a second optical element 72 of the polarizing unit 7 arearranged to have their optical axes perpendicular to each other, and areflection mirror 73 is disposed between these optical elements 71 and72 at an angle of 45 degrees with respect to both the optical elements71 and 72. The other constituents of the polarizing lighting device 60Aare identical with those of the polarizing lighting device 60, and arethus not specifically described here.

A blue-green light reflection dichroic mirror 401 of the colorseparation optical system 400 causes a red light component of the lightflux emitted from the polarizing lighting device 60A to be transmitted,whereas causing blue and green light components to be reflected. The redlight component is reflected from a reflection mirror 403 and reaches ared-light liquid-crystal device 411 via a field lens 415. The greenlight component is reflected by a green light reflection dichroic mirror402 of the color separation optical system 400 and reaches a green-lightliquid-crystal device 412 via a field lens 416. Each of the field lenses415 and 416 has the function of converting the incident light flux to alight flux parallel to its center axis.

The length of the optical path of the blue light component is greaterthan those of the optical paths of the other two color components, sothat a light-leading optical system 430 including a relay lens systemconsisting of an entrance lens 431, a relay lens 432, and an exit lens433 is provided for the blue light component. The blue light componentpasses through the green light reflection dichroic mirror 402, goesthrough the entrance lens 431, is reflected by a reflection mirror 435to be led to and focused on the relay lens 432, is reflected again by areflection mirror 436 to be led to the exit lens 433, and eventuallyreaches a blue-light liquid-crystal device 413. The exit lens 433 hasthe same function as those of the field lenses 415 and 416.

The three liquid-crystal devices 411, 412, and 413 are transmissionliquid-crystal panels (also called `liquid-crystal light bulbs`) thatmodulate the respective color rays to represent respective imageinformation and cause such modulated color rays to enter the crossdichroic prism 450. The cross dichroic prism 450 has a dielectricmulti-layered film for reflecting red light and a dielectricmulti-layered film for reflecting blue light, which are formed in across shape, to combine the modulated color light fluxes to create acolor image. The color image is expanded and projected on a screen 470as a projection image by the projection lens 460.

The projector-type display apparatus 80 uses the polarizing lightingdevice 60A with the two lamp units 21A and 21B and accordingly formsbright projection images.

In accordance with one preferable structure, a driving circuit of thepolarizing lighting device 60A may simultaneously turn on both the lampunits 21A and 21B or selectively turn on either one of the lamp units21A and 21B. For example, when the required illuminance is relativelylow, only one lamp unit is turned on. This structure enables projectionimages of optimum brightness to be formed according to thecircumferences.

The projector-type display apparatus 80 of the embodiment includes theliquid-crystal devices for modulating light fluxes of a singlepolarization type. When the light fluxes of random polarization areoutput from a conventional lighting device to the liquid-crystaldevices, approximately half the light fluxes of random polarization areabsorbed and changed to heat by polarizing plates (not shown). Thisworsens the utilization efficiency of light and requires a large-sized,rather noisy cooling device for cooling the polarizing plates. Theprojector-type display apparatus 80 of the embodiment, on the otherhand, effectively solves these problems. In the projector-type displayapparatus 80 of the embodiment, the polarizing lighting device 60Acauses light fluxes on a single polarization type, for example, only thep-polarized light fluxes, to be subjected to a rotation of thepolarizing plane in a λ/2 phase difference plate and converted to theother type of polarized light fluxes, for example, s-polarized lightfluxes. The light fluxes of substantially identical polarizingdirections are accordingly led to the three liquid-crystal devices 411,412, and 413. This structure of the embodiment remarkably reducesabsorption of light by the polarizing plates and enhances theutilization efficiency of light, thereby producing bright projectionimages.

The polarizing lighting device 60A used here as the lighting deviceincludes the shielding plate 730 arranged inside the second opticalelement 72. This arrangement effectively prevents light fluxes of theother polarization type unrequired for the display of the liquid-crystaldevices from being present in the light output from the polarizinglighting device 60A for illumination. This remarkably decreases theabsorption of light by polarizing plates (not shown) arranged on thelight-entering side of the three liquid-crystal devices 411, 412, and413 and thereby remarkably lessens the heat due to the absorption oflight, thus significantly reducing the size of a cooling device forpreventing a temperature increase of the polarizing plates and theliquid-crystal devices.

A small-sized cooling device is accordingly sufficient even for theprojector-type display apparatus that utilizes extremely powerful lightsource lamps to display extremely bright projection images. Thisstructure reduces the noise of the cooling device and realizes a still,high-performance projector-type display apparatus.

In the polarizing lighting device 60A, the second optical element 72spatially separates the two different polarized light fluxes in thelateral direction (in the x direction). This structure does not wastethe quantity of light but efficiently illuminates the liquid crystaldevices of a wide rectangular shape.

Although the polarization converting optical elements are incorporatedin the polarizing lighting device 60A, the structure of the embodimenteffectively prevents the extension of the width of light fluxes outputfrom the array of polarization separating units 740. This means thatthere exists substantially no light entering the liquid-crystal deviceswith a large angle for illumination. This structure realizes brightprojection images without an extremely large-diametral projection lenssystem having a small F number, thereby effectively reducing the size ofthe projector-type display apparatus.

In this embodiment, the cross dichroic prism 450 is used as a colorcombining means. This further reduces the size of the apparatus. Sincethe optical paths between the respective liquid crystal devices 411,412, and 413 and the projection lens system 460 are short, even arelatively small-diametral projection lens system can produce brightprojection images. Although the length of the optical path of one colorray is different from those of the other two color rays, thelight-leading optical system 430 including the relay lens systemconsisting of the entrance lens 431, the relay lens 432, and the exitlens 433 is provided for the blue light component having the longestoptical path. This effectively prevents unevenness of colors.

The projector-type display apparatus may utilize a mirror optical systemusing two dichroic mirrors as the color combining means. The polarizinglighting device of the embodiment can also be incorporated in such amodified structure. Like the above embodiment, the modified structurehas high utilization efficiency of light and produces bright,high-quality projection images.

Although the light fluxes of random polarization are converted to thes-polarized light fluxes in this embodiment, they may be converted tothe p-polarized light fluxes.

(Fourth Embodiment)

FIG. 13 schematically illustrates another polarizing lighting deviceembodying the present invention. Like the polarizing lighting devices 60and 60A, a polarizing lighting device 90 of this embodiment includes alight source unit 2 and a polarizing unit 7'. Two lamp units 21A and 21Bof the light source unit 2 are arranged in parallel in the y-axisdirection to have their lamp optical axes 21L parallel to a systemoptical axis 90L. Like the polarizing unit 7, the polarizing unit 7' hasthe function of converting the light fluxes of random polarizationemitted from the light source unit 2 to light fluxes of substantiallyidentical polarizing directions and causing the illumination area 4 tobe illuminated substantially uniformly with the light fluxes ofsubstantially identical polarizing directions.

Like the first optical element 71 shown in FIG. 8, a first opticalelement 71' included in the polarizing unit 7' is a lens array in whichflux division lenses 711' are arranged in a 4×4 matrix. The fluxdivision lenses 711' include four kinds of rectangular flux divisionlenses 711a', 711b', 711c', and 711d' according to the position in the ydirection. The flux division lenses 711a', 711b', 711c', and 711d' areeccentric lenses which deviate the centers of the light fluxes outputfrom the respective lenses only in the y direction.

Like the second optical element 72 shown in FIG. 8, a second opticalelement 72' includes a condenser lens array 720', a shielding plate730', an array of polarization separating units 740', a selective phasedifference plate 750', and a superposing lens 760'. Like the condenserlens array 720 (FIG. 8), the condenser lens array 720' includescondenser lenses 721' arranged in a 4×4 matrix corresponding to thefirst optical element 71'. Like the flux division lenses 711', thecondenser lenses 721' include four kinds of rectangular condenser lenses721a', 221b', 721c', and 721d' having different amounts of eccentricityaccording to the position in the y direction. The condenser lenses 721'have smaller dimensions in the y direction than the flux division lenses711', so that the condenser lens array 720' has a smaller dimension inthe y direction than the first optical element 71'.

Like the array of polarization separating units 740 shown in FIG. 8, thearray of polarization separating units 740' include a plurality ofpolarization separating units 770' arranged in a matrix. Like thepolarization separating unit 770 shown in FIG. 11, the polarizationseparating unit 770' has a polarization separating surface 741' and areflection surface 742' aligned in the x direction to separate theincident light fluxes of random polarization in the x direction to twodifferent polarized light fluxes of different polarizing directions.Corresponding to the dimension of the condenser lens 721', the dimensionof the polarization separating unit 770' in the y direction is smallerthan that of the polarization separating unit 770 of FIG. 11. Similarly,corresponding to the dimension of the condenser lens array 720', thedimension of the array of polarization separating units 740' in the ydirection is smaller than that of the array of polarization separatingunits 740.

The shielding plate 730', the selective phase difference plate 750', andthe superposing lens 760' are respectively arranged to have thedimensions corresponding to that of the array of polarization separatingunits 740'.

As discussed above, the polarizing lighting device 90 of this embodimentis characterized by the structure of the respective constituents of thefirst optical element 71' and the second optical element 72'. The basicarrangements and functions of the respective constituents are similar tothose of the first optical element 71 and the second optical element 72shown in FIG. 8, and are thus not specifically described here. Thefollowing further describes the structural characteristics of therespective constituents of the first optical element 71' and the secondoptical element 72'.

The outer shape of the flux division lenses 711' is substantiallysimilar to the shape of the illumination area 4, in order to enable theillumination area 4 to be illuminated most efficiently with theintermediate light fluxes divided by the flux division lenses 711'. Whenthe polarizing light device 90 of the embodiment is applied to aprojector-type display apparatus, such as the projector-type displayapparatus 80 (FIG. 12), the illumination area 4 corresponds to theliquid-crystal devices 411, 412, and 413. The aspect ratio (width tolength) of the display area is 4 to 3 in the liquid-crystal devices 411,412, and 413. In this embodiment, the length of the flux division lens711' is three quarters its width LW in the lateral direction (in the xdirection). The length of the condenser lens 721' is two quarters itswidth LW. The reason of these dimensions is given below.

FIG. 14 shows converged images formed by the flux division lenses 711'and the condenser lenses 721'. FIG. 14(A) illustrates part of thecondenser lens array 720 and the array of polarization separating units740 included in the polarizing lighting device 60 of FIG. 8, seen fromthe y direction. FIG. 14(B) illustrates the same, seen from the zdirection. Although the condenser lenses 721 are drawn while shifted alittl in the y direction for the clarity of illustration in FIG. 14(B),they are not so shifted in the actual state. The intermediate light flux712 passing through the condenser lens 721 is focused at the substantialcenter on the polarization separating surface 741 included in thepolarization separating unit 770 by means of the flux division lens 721(see FIG. 8) and the condenser 711. The converged image 713 isaccordingly formed on the polarization separating surface 741.Similarly, a converged image 713' having substantially the same size asthat of the converged image 713 is formed on the reflection surface 742.Since the distance between the entrance plane and the exit plane of thepolarization separating unit 770 is relatively small, the sizes of theincident light flux and the output light flux of the polarizationseparating unit 770 are also substantially identical with the size ofthe converged image 713. The following description is therefore madeusing the size of the converged image 713 in the place of the sizes ofthe incident light flux and the output light flux of the polarizationseparating unit 770.

If the intermediate light flux 712 were not focused but simply separatedinto the p-polarized light flux and the s-polarized light flux, thetotal width of the light fluxes after the separation would be doubledand makes the optical system undesirably bulky. In the polarizinglighting device 60, in order to prevent the optical system from beingbulky, the reflection surface 742 of the polarization separating unit770 is disposed in the space which is produced by focusing the pluralityof intermediate light fluxes 712 and where no light exists. In thepolarizing lighting device 60, as shown in FIG. 14(B), the dimension inthe x direction of a projection of the polarization separating surface741 on the x-y plane is substantially identical with the dimensions inthe x direction of projections of the converged images 713 and 713' onthe x-y plane, and is approximately equal to half the width LW of thecondenser lens 721 in the x direction. Similarly, the dimension in the xdirection of a projection of the reflection surface 742 on the x-y planeis approximately equal to half the width LW. The dimension in the ydirection of the projection of the polarization separating surface 741on the x-y plane is approximately equal to the dimension, (LW·3/4), ofthe condenser lens 721 in the y direction. Similarly, the dimension inthe y direction of the projection of the reflection surface 742 on thex-y plane is approximately equal to the dimension (LW·3/4).

The converged images 713 and 713' projected on the x-y plane are hereapproximated to be virtually circular. As shown in FIG. 14(B), in thearea of the polarization separating unit 770 in the y direction, thearea between the upper end and the position apart therefrom in the ydirection by 1/8 of the width LW and the area between the lower end andthe position apart therefrom in the y direction by 1/8 of the width LWare hardly utilized (substantially no light exists in these areas). Inother words, the condenser lens 721 and the polarization separating unit770 can be reduced by the size corresponding to one quarter of the widthLW in the y direction. From this reason, in the polarizing lightingdevice 90 of the embodiment, the dimension of the condenser lens 721' inthe y direction is made smaller than the dimension (LW·3/4) of thecondenser lens 721 in the y direction by (LW·1/4) as shown in FIG.14(C).

The reduction of the dimension of the condenser lens 721' in the ydirection to LW/2 results in reducing the size of the whole condenserlens array 720' in the y direction. For application of this condenserlens array 721', the condenser lenses 721' and the flux division lenses711' should be formed as discussed below.

FIG. 15 illustrates structures of the flux division lenses 711' and thecondenser lenses 721'. The flux division lens 711' is a rectangular lensprepared by cutting a known concentric lens 700 by a width LW about anoptical axis LC in the x direction and at either one of two positions711a' and 711b' shown in FIG. 15(A) in the y direction. The fluxdivision lens 711' is accordingly formed as an eccentric lens in whichthe positions of the lens center and the optical axis are different inthe y direction. The first flux division lens 711a' is cut in an x-zplane including the position of the lens center (optical axis) LC of theconcentric lens 700 and the position apart from the lens center LCupward in the y direction by a distance (LW·3/4). The second fluxdivision lens 711b' is cut in the x-z plane including the position apartfrom the lens center LC downward in the y direction by a distance (LW/4)and the position apart from the lens center LC upward in the y directionby a distance (LW·2/4). The other flux division lenses 711c' and 711d'shown in FIG. 13(B) are the upside-down of the flux division lenses711a' and 711b'.

The condenser lens 721' is a rectangular lens prepared by cutting theknown concentric lens 700 by the width LW about the optical axis LC inthe x direction and at either one of two positions 721a' and 721b' shownin FIG. 15(B) in the y direction. The condenser lens 721' is accordinglyformed as an eccentric lens in which the positions of the lens centerand the optical axis are shifted in the y direction. The first condenserlens 721a' is cut in the x-z plane including the position apart from thelens center LC downward in the y direction by a distance (LW·5/8) andthe position apart from the lens center LC downward in the y directionby a distance (LW/8). The second condenser lens 721b' is cut in the x-zplane including the position apart from the lens center LC downward inthe y direction by a distance (LW·3/8) and the position apart from thelens center LC upward in the y direction by a distance (LW·1/8).

FIG. 16 shows the positional relationship between the flux divisionlenses 711' and the condenser lenses 721' in the y direction. The fluxdivision lens 711a' and the corresponding condenser lens 721a' arearranged in such a manner that the position of a lens center 711a' (GC)of the flux division lens 711a' coincides with the position of anoptical axis 721a' (OC) of the condenser lens 721a' and that theposition of an optical axis 711a' (OC) of the flux division lens 711a'coincides with the position of a lens center 721a' (GC) of the condenserlens 721a'. Similarly, the flux division lens 711b' and thecorresponding condenser lens 721b' are arranged in such a manner thatthe position of a lens center 711b' (GC) of the flux division lens 711b'coincides with the position of an optical axis 721b' (OC) of thecondenser lens 721b' and that the position of an optical axis 711b' (OC)of the flux division lens 711b' coincides with the position of a lenscenter 721b' (GC) of the condenser lens 721b'.

The light flux entering the flux division lens 711a' is divided intointermediate light fluxes 712a' and deflected to pass through theapproximate center of the corresponding condenser lens 721a'. For thesimplicity of explanation, only the primary ray is shown as for theintermediate light fluxes 712a' divided by the flux division lens 711a'.The deflected intermediate light fluxes 712a' pass through the condenserlens 721a' and are deflected to be parallel to the course of theincident light flux of the flux division lens 711a', that is, to makethe primary ray substantially parallel to a light source optical axis90R. The output position of the intermediate light fluxes 712a' from thecondenser lens 721a' is shifted from the output position of theintermediate light fluxes 712a' from the flux division lens 711a' inparallel toward the light source optical axis 90R. Similarly, the outputposition of the intermediate light fluxes 712b', which is divided by theflux division lens 711b', from the condenser lens 721b' is shifted fromthe output position of the intermediate light fluxes 712b' from the fluxdivision lens 711b' in parallel toward the light source optical axis90R. Deflection by the first optical element 71' and the condenser lensarray 720' causes the optical path of the plurality of intermediatelight fluxes 712' output from the condenser lens array 720' to beshifted in parallel toward the light source optical axis 90R in the ydirection. The whole light fluxes passing through the condenser lensarray 720' are accordingly compressed about the light source opticalaxis 90R in the y direction with respect to the light fluxes enteringthe first optical element 71'. The condenser lens array 720' having thesmaller dimension in the y direction than that of the condenser lensarray 720 (FIG. 8) can be used when the flux division lenses 711' andthe condenser lenses 721' are formed to be appropriate eccentric lensesand arranged them in the appropriate positions as described above.

The polarizing lighting device 90 of the embodiment exerts the followingeffects. FIG. 17 illustrates the light entering the projection lens 460when the polarizing lighting device 90 is applied to a projector-typedisplay apparatus. The projection lens 460 effectively projects only thelight component entering a lens pupil 460e shown in FIG. 17(A) on aprojection plane, while not projecting the light component enteringoutside the lens pupil 460e. The incident angle range allowingprojection (may also be called the `entrance angle`) varies as theposition within the lens pupil 460e. The incident angle range is thelargest at the center of the lens pupil 460e and decreases toward theperiphery, so that the utilization efficiency of light in the projectionlens is the highest at the center of the lens and worsens toward theperiphery.

FIG. 17(B) shows intensity distributions of light 21ALP and 21BLP whenthe rays emitted from the lamp units 21A and 21B pass through thecondenser lens array 720 and enter the lens pupil 460e of the projectionlens 460, where the lamp units 21A and 21B of the polarizing lightingdevice 60A included in the projector-type display apparatus 80 shown inFIG. 12 are arrayed in the y direction like the polarizing lightingdevice 90. The intensity distributions of light 21ALP and 21BLP areshown as contours. As shown in FIG. 17(B), the intensity distribution oflight 21ALP from the lamp unit 21A and the intensity distribution oflight 21BLP from the lamp unit 21B have distribution centers 21ALC and21BLC that are shifted respectively upward and downward from a center460L of the projection lens. In the structure that the lamp units 21Aand 21B are arrayed in the x direction, on the other hand, the intensitydistribution of light 21ALP from the lamp unit 21A and the intensitydistribution of light 21BLP from the lamp unit 21B have the distributioncenters 21ALC and 2113LC that are shifted respectively leftward andrightward from the center 460L of the projection lens. As mentionedpreviously (see FIG. 4), the intensity of light is the highest in thevicinity of the distribution centers 21ALC and 21BLC and abruptlydecreases toward the periphery in the intensity distributions of light21ALP and 21BLP of the lamp units 21A and 21B. The utilizationefficiency of light is the highest on the center of the projection lensand decreases toward the periphery as discussed above. When two lampunits are used as the light source of the lighting device, although thequantity of light from the lighting device increases as a whole, theutilization efficiency of light is not sufficiently high in the wholeprojector-type display apparatus since the centers 21ALC and 21BLC ofthe intensity distributions of light from the two lamp units are apartfrom the lens center 460L.

In the projector-type display apparatus with the polarizing lightingdevice 90 of the embodiment applied thereto, as shown in FIG. 17(C), thefunction of the first optical element 71' and the condenser lens array720' compresses an intensity distribution of light 21ALP' from the lampunit 21A and an intensity distribution of light 21BLP' from the lampunit 21B in the y direction around the center 460L of the projectionlens, compared with the intensity distributions of light 21ALP and 21BLPshown in FIG. 17(B). This means that respective distribution centers21ALC' and 21BLC' are closer to the center 460L of the projection lensthan the distribution centers 21ALC and 21BLC shown in FIG. 17(B).Compared with the projector-type display apparatus with the polarizinglighting device 60A applied thereto, the projector-type displayapparatus with the polarizing lighting device 90 of the embodimentapplied thereto has the improved utilization efficiency of light in theprojection lens and the possibility of projecting and displayingbrighter projection images.

In accordance with one modified structure, the condenser lenses 721' arealso arranged in the areas filled with slant lines in FIG. 17(C) and thenumber of arrays of the flux division lenses 711' as well as the area ofthe reflectors in the lamp units 21A and 21B is increasedcorrespondingly. This enables projection and display of further brighterprojection images.

A condenser lens array 720" shown in FIG. 18 includes condenser lenses721", which are arranged in the circumferential portion in the xdirection and are smaller in the y direction than the condenser lenses721' of the central portion. In case that the lamp units 21A and 21B ofthe polarizing lighting device 60A are arrayed in the y direction in theprojector-type display apparatus 80 shown in FIG. 12, the convergedimages formed in the vicinity of the condenser lens array 720' by aplurality of intermediate light fluxes actually have the shapes whichvaries according to their positions as shown in FIG. 19. The lightfluxes closer to the lamp center form larger converged images, whereasthose farther from the lamp center form smaller converged images. Thecondenser lenses 721' apart from the lamp centers 21ALC and 21BLC of thelamp units 21A and 21B are reduced in size in the y direction as shownin FIG. 18. This further improves the utilization efficiency of theprojection lens regarding the light fluxes passing through theserectangular lenses, and has the possibility of projecting and displayingbrighter projection images. In the example of FIG. 18, the left-most rowand the right-most row are reduced in size among the four rows ofrectangular lenses (condenser lenses) in the condenser lens array 720'.The reduction of the size is, however, not restricted to thisarrangement, but different rows may have different sizes according tothe dimensions of the converged images. Not only the dimension of therectangular lenses in the y direction but the dimension of therectangular lenses of each row in the x direction may be changedaccording to the size of the converged images in the x direction. Inanother example, the respective rectangular lenses may have differentdimensions in the y direction and the x direction according to the sizeof the converged images.

In the polarizing lighting device 90 of the embodiment, the aspect ratioof the condenser lenses 721' is two to one, whereas the aspect ratio ofthe flux division lenses 711' is four to three. The aspect ratio is,however, not restricted to these values. The aspect ratio of thecondenser lenses should be set smaller than the aspect ratio of the fluxdivision lenses, in order to enable the condenser lens array to includeat least most of the converged images, which are converged and formed onthe polarization separating surfaces and the reflection surfaces of thepolarization separating units by the flux division lenses.

In the polarizing lighting device 90 of the embodiment, the dimension ofthe condenser lenses 721' in the y direction is set smaller than thedimension of the flux division lenses 711' in the y direction. Thisstructure is also effective in the lighting device having a single lampunit as the light source.

In this embodiment, the lamp units having the side-cut reflectors 220Aand 220B as described in the first embodiment are used as the lamp units21A and 21B. The lamp units having reflectors without any side cuts,however, exert the similar effects to those discussed above.

Like the polarizing lighting device 60 of the second embodiment (FIG.8), the polarizing lighting device 90 of this embodiment includes anintegrator optical system and a polarizing unit and thereby has theeffects due to the integrator optical system and the polarizing unit asdescribed in the second embodiment.

The polarizing lighting device 90 of this embodiment may have thestructure which allows the two light source lamps to be turned on andoff selectively. This structure enables the brightness of light to beadjusted in multiple steps, thereby attaining the required brightnessand efficient power consumption.

Further, application of the lamp units including light source lamps ofdifferent spectra to a color projector-type display apparatus improvesthe color reproducibility.

(Fifth Embodiment)

FIG. 20 illustrates the positional relationship between dichroic mirrorsand lamp units in a projector-type display apparatus including anotherlighting device embodying the present invention. FIGS. 20(A) and 20(B)schematically illustrate a red-light liquid-crystal device illuminatedwith red light fluxes which are separated from the light fluxes emittedfrom a lighting device 100 by a blue-green light reflection dichroicmirror 401 functioning as a color separating optical element. Althoughonly the optical elements, a cross dichroic prism 450, the red-lightliquid-crystal device 411, the blue-green light reflection dichroicmirror 401, and the lighting device 100, are shown in alignment forconvenience in FIGS. 20(A) and 20(B), the only difference from theprojector-type display apparatus 80 shown in FIG. 12 is that thepolarizing lighting device 60A is replaced by the lighting device 100 ofthe embodiment.

As shown in FIGS. 20(A) and 20(B), the blue-green light reflectiondichroic mirror 401 functioning as a color separating optical element isarranged substantially perpendicular to an x-z plane and atpredetermined angles to a y-z plane and an x-y plane.

The lighting device 100 of the embodiment has a light source unit 110,which includes first and second lamp units 110A and 110B of identicalstructure and substantially the same size. The lamp units 110A and 110Brespectively have light source lamps 120A and 120B and reflectors 130Aand 130B of a paraboloidal, ellipsoidal, or circular shape. Like thefirst embodiment, the reflectors 130A and 130B of this embodiment haveside cuts. The lamp units 110A and 110B are arranged virtually along they axis. Namely the lamp units 110A and 110B are arrayed in the directionperpendicular to the direction of two output rays from the dichroicmirror 401.

FIG. 22 shows color separation characteristics of the blue-green lightreflection dichroic mirror 401. When the light enters the blue-greenlight reflection dichroic mirror 401 at a predetermined angle, thedichroic mirror 401 allows only a red light component (not lower thanapproximately 600 nm) of the incident light to be transmitted, whilecausing the other light components (a blue light component and a greenlight component) to be reflected (the characteristics shown by the solidline in FIG. 22). Such color separation characteristics varies with theincident angle of the light entering the blue-green light reflectiondichroic mirror 401. In case that the light does not enter theblue-green light reflection dichroic mirror 401 at the predeterminedincident angle, the red light component led to the red-lightliquid-crystal device 411 shows a color shift.

In case that the lamp units 110A and 110B are arrayed in the x-axisdirection as shown in FIG. 21, incident angles θA1 and θB1 of the raysemitted from the lamp units 110A and 110B to the blue-green lightreflection dichroic mirror 401 are different from each other anddeviated from the predetermined angle. For example, the light emittedfrom the lamp unit 110A accordingly has the characteristics shown by thebroken line in FIG. 22, which are different from the desired colorseparation characteristics shown by the solid line in FIG. 22. The lightemitted from the lamp unit 110B, on the other hand, has thecharacteristics shown by the one-dot chain line in FIG. 22, which arealso different from the desired color separation characteristics shownby the solid line in FIG. 22. The respective output rays have differentcolor separation characteristics. This causes a color shift in the redlight component that passes through the dichroic mirror 401 and is ledto the red-light liquid crystal device 411.

In the lighting device 100 of the embodiment, on the other hand, thelamp units 110A and 110B are arrayed substantially along the y axis asshown in FIGS. 20(A) and 20(B). This arrangement enables the raysemitted from the lamp units 110A and 110B to enter the blue-green lightreflection dichroic mirror 401 at an identical incident angle. Thismakes the respective output rays have the same desired color separationcharacteristics, and thereby reduces the color shift of the red lightcomponent for illuminating the red-light liquid-crystal device 411.

This arrangement also enables the rays emitted from the lamp units 110Aand 110B to enter a green light dichroic mirror 402 at an identicalincident angle θ, like the blue-green light reflection dichroic mirror401. This accordingly reduces the color shift of the light componentsfor illuminating a green-light liquid crystal device 412 and ablue-light liquid-crystal device 413. The lighting device 100 of theembodiment illuminates liquid-crystal devices with rays of uniformbrightness and no color shift.

This arrangement has similar effects on a red light reflection dichroicsurface 451 and a blue light reflection dichroic surface 452 of thedichroic prism 450 as shown in FIGS. 20(A) and 20(B). Namely the raysemitted from the lamp units 110A and 110B to the dichroic surfaces 451and 452 have identical incident angles θA2 and θB2. The lighting device100 of the embodiment incorporated in the projector-type displayapparatus effectively reduces the color shift in projection images.

The lighting device 100 of the embodiment includes two lamp units andthereby has the enhanced quantity of output light, like the embodimentsdescribed above.

As described above, the projector-type display apparatus with thelighting device 100 of the embodiment incorporated therein can produceprojection images that are uniformly bright over the whole projectionarea and have substantially no color shift.

In this embodiment, the lamp units having the side-cut reflectors 130Aand 130B as described in the first embodiment are used as the lamp units110A and 110B. The lamp units having reflectors without any side cuts,however, attain the similar effects to those described above.

The lighting device 100 of the embodiment may further include anintegrator optical system and a polarizing unit described above. In thiscase, the lighting device 100 has the effects due to the integratoroptical system and the polarizing unit, in addition to the aboveeffects. Namely the lighting device 100 attains the enhanced brightnessand reduced unevenness of illuminance as well as the reduced color shiftin projection images.

The lighting device 100 of this embodiment may have the structure whichallows the two light source lamps to be turned on and off selectively.This structure enables the brightness of light to be adjusted inmultiple steps if required, thereby attaining the required brightnessand efficient power consumption. In the lighting device 100 of theembodiment, since the spectroscopic characteristics of the dichroicmirror and the prism do not change even when only one lamp is turned on,the projection images obtained have some decrease in brightness but arefree of a color tone change.

(Other Embodiments of the Present Invention)

Although the third embodiment has referred to the projector-type displayapparatus 80 with the polarizing lighting device 60A incorporatedtherein, which has the same structure as the polarizing lighting device60, the lighting device 1 shown in FIG. 1 may be incorporated in theprojector-type display apparatus 80 in place of the polarizing lightingdevice 60A. In this case, the small-sized light source unit reduces thesize of the whole projector-type display apparatus.

In all the above embodiments, the lighting device of the presentinvention is applied to the projector-type display apparatus withtransmission liquid-crystal devices. The lighting device of the presentinvention is also applicable to the projector-type display apparatuswith reflection-type liquid-crystal devices.

The present invention is applicable to both front-projection type andrear-projection type display apparatuses. The front-projection typeprojects images from the side of observing the projection plane, whereasthe rear-projection type projects images from the opposite side.

The present invention is not restricted to the above embodiments ortheir modified examples, but there may be many other modifications,changes, and alterations without departing from the scope or spirit ofthe main characteristics of the present invention.

The lighting device of the present invention is applicable to a varietyof projector-type display apparatuses. The projector-type displayapparatus of the present invention may be used to project and displayimages output from a computer or images output from a video cassetterecorder on a screen.

What is claimed is:
 1. A lighting device comprising a lamp unit having alight source lamp and a reflector for reflecting light emitted from thelight source lamp, the lighting device further comprising:a plurality ofthe lamp units arrayed adjacent to one another; wherein the reflector ofeach lamp unit has a shape obtained through cutting a concave surface ofreflection on at least one end adjoining to another lamp unit by a planesubstantially perpendicular to a direction of the array of the lampunits, the reflector has a shape obtained through cutting both ends ofthe concave surface of reflection by the plane substantiallyperpendicular to the direction of the array of the lamp units, and adistance between both cut faces is approximately half a diameter of anopening of the concave surface of reflection.
 2. A lighting device inaccordance with claim 1, wherein the plurality of lamp units are arrayedin one direction substantially perpendicular to the optical axis of thelight source lamp.
 3. A lighting device in accordance with claim 1,wherein the plurality of lamp units are arrayed in two directionssubstantially perpendicular to the optical axis of the light sourcelamp.
 4. A lighting device in accordance with claim 1, wherein thereflectors included in the plurality of lamp units are opticallyintegrated with one another.
 5. A lighting device in accordance withclaim 1, the lighting device further comprising:a control circuit forselectively turning on any of the light source lamps included in theplurality of lamp units.
 6. A lighting device in accordance with claim1, wherein the light source lamps included in the plurality of lampunits emit respective light of different wavelength distributioncharacteristics.
 7. A lighting device in accordance with claim 1, thelighting device further comprising:an integrator optical system having afirst lens plate including a plurality of lenses and a second lens plateincluding a plurality of lenses, wherein the first lens plate spatiallydivides the light emitted from the light source lamp by the plurality oflenses included therein to produce a plurality of intermediate lightfluxes, which are focused as secondary light source images in thevicinity of entrance planes of the plurality of lenses included in thesecond lens plate, output via the plurality of lenses included in thesecond lens plate, and superposed on a predetermined illumination area.8. A lighting device in accordance with claim 7, the lighting devicefurther comprising:polarizing means for converting light fluxes outputfrom the second lens plate to light fluxes of a single polarization typehaving identical polarizing directions and outputting the light fluxesof the single polarization type, the polarizing means comprising:polarization separating means for separating the light fluxes outputfrom the second lens plate into light fluxes of two polarization typeshaving different polarizing directions; and polarization convertingmeans for converting the polarizing direction of one of the light fluxesof the two polarization types obtained by the polarization separatingmeans to the polarizing direction of the other of the light fluxes ofthe two polarization types, wherein the predetermined illumination areais illuminated with the polarized light fluxes of the single type havingidentical polarizing directions obtained by the polarizing means.
 9. Aprojector comprising:a lighting device in accordance with claim 1;modulation means for modulating light emitted from the lighting deviceresponsive to image information; and a projection optical system forprojecting a modulated light flux obtained by the modulation means ontoa projection plane.
 10. A projector in accordance with claim 9, furthercomprising:color separation means for separating the light emitted fromthe lighting device into at least two color light fluxes; a plurality ofthe modulation means for modulating the respective color light fluxesseparated by the color separation means; and color combining means forcombining the color light fluxes modulated by the plurality ofmodulation means, wherein a composite light flux obtained by the colorcombining means is projected on the projection plane via the projectionoptical system.
 11. A lighting device for illuminating an illuminationarea of a substantially rectangular shape having sides parallel toeither of a first direction and a second direction which aresubstantially perpendicular to each other, the lighting devicecomprising:a light source; a first lens plate having a plurality ofsmall lenses for dividing a light flux emitted from the light sourceinto a plurality of partial light fluxes and condensing the plurality ofpartial light fluxes; a second lens plate having a plurality of smalllenses on which the plurality of partial light fluxes are incident;polarizing means comprising polarization separating means for separatingeach of the plurality of partial light fluxes output from the secondlens plate into light fluxes of two polarization types having differentpolarizing directions, and polarization converting means for convertingthe polarizing direction of one of the light fluxes of the twopolarization types obtained by the polarization separating means to thepolarizing direction of the other of the light fluxes of the twopolarization types, the polarizing means thereby converting theplurality of partial light fluxes to plural light fluxes of a singlepolarization type having substantially identical polarizing directionsand outputting the plural light fluxes of the single polarization type;and superposing means for superposing the plural polarized light fluxesoutput from the polarizing means to illuminate the illumination area,wherein the polarization separating means is arranged to cause the lightfluxes of two polarization types to be spatially separated along thefirst direction of the illumination area, wherein each the small lens ofthe first lens plate has a substantially rectangular shape whenprojected on a plane perpendicular to a central optical axis of the eachsmall lens, the substantially rectangular shape having an aspect ratiothat is virtually equal to an aspect ratio of the illumination area, theplurality of partial light fluxes output from the small lenses beingincident on corresponding small lenses of the second lens plate, whereineach the small lens of the second lens plate has a substantiallyrectangular shape when projected on a plane perpendicular to a centraloptical axis of the each small lens, the substantially rectangular shapehaving an aspect ratio that is smaller than the aspect ratio of theillumination area, and wherein the aspect ratio is defined by a ratio ofa length of the side parallel to the second direction to a length of theside parallel to the first direction.
 12. A lighting device inaccordance with claim 11, wherein the light source comprises a pluralityof lamp units arrayed in the second direction, each the lamp unit havinga light source lamp and a reflector for reflecting light emitted fromthe light source lamp.
 13. A lighting device in accordance with claim11, wherein the aspect ratio of the each small lens of the second lensplate is approximately 1/2.
 14. A lighting device in accordance withclaim 11, wherein the plurality of small lenses included in the secondlens plate are arranged in a plurality of rows along the seconddirection, and dimensions along the second direction of the small lensesin each row are reduced with their distances from a center position ofthe light flux emitted from the light source.
 15. A lighting device inaccordance with claim 12, wherein the reflector of each lamp unit has ashape obtained through cutting a concave surface of reflection on atleast one end adjoining to another lamp unit by a plane substantiallyperpendicular to a direction of the array of the lamp units.
 16. Aprojector comprising:a lighting device in accordance with claim 11;modulation means for modulating light emitted from the lighting deviceresponsive to image information; and a projection optical system forprojecting a modulated light flux obtained by the modulation means ontoa projection plane.
 17. A projector in accordance with claim 16, furthercomprising:color separation means for separating the light emitted fromthe lighting device into at least two color light fluxes; a plurality ofthe modulation means for modulating the respective color light fluxesseparated by the color separation means; and color combining means forcombining the color light fluxes modulated by the plurality ofmodulation means, wherein a composite light flux obtained by the colorcombining means is projected on the projection plane via the projectionoptical system.
 18. A lighting device in accordance with claim 12,wherein the aspect ration of the each small lens of the second lensplate is approximately 1/2.
 19. A lighting device in accordance withclaim 12, wherein the plurality of small lenses included in the secondlens plate are arranged in a plurality of rows along the seconddirection, and dimensions along the second direction of the small lensesin each row are reduced with their distances from a center position ofthe light flux emitted from the light source.
 20. A projectorcomprising:a lighting device in accordance with claim 12; modulationmeans for modulating light emitted from the lighting device responsiveto image information; and a projection optical system for projecting amodulated light flux obtained by the modulation means onto a projectionplane.
 21. A projector in accordance with claim 20, furthercomprising:color separation means for separating the light emitted fromthe lighting device into at least two color light fluxes; a plurality ofthe modulation means for modulating the respective color light fluxesseparated by the color separation means; and color combining means forcombining the color light fluxes modulated by the plurality ofmodulation means, wherein a composite light flux obtained by the colorcombining means is projected on the projection plane via the projectionoptical system.